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Inherited Disorders and Birth Defects

Shared Genes Through Friedreich`s Ataxia

03/09/2009

Question:

My mother and father had 7 children. Two of which have Osteo Geneisis Imperfecta: one being myself, and my sister has Friedreich`s ataxia. Now I`m no expert but seems awfully peculiar to have 2 seperate rare afflictions in the family. My sisters Friedreich`s ataxia didn`t strike until she was 12 years old. Is that normal or are most people struck at birth. My question as well is do these 2 afflictions occur on the gene or gene sequences. Are they somehow intertwined? Like I said, I`m no expert but my dad had Osteo genesis imperfecta. Or maybe this is more prevelent than I know. Please any help is appreciated. Just seems odd.

Answer:

Osteogenesis imperfecta (OI) and Friedreich ataxia (FRDA) are 2 different genetic diseases - the genes that cause these 2 diseases are entirely different, are on different chromosomes and have a different pattern of inheritance. While it is not common to see 2 different genetic diseases in one family, it does happen. I am not aware of any connection between the two disorders.

As you know, Osteogenesis Imperfecta (OI) (“brittle bone disease”) is a group of genetic disorders that cause bones to break (fractures) very easily - sometimes with very little or no trauma. Other problems that can happen include problems with the enamel of the teeth (dentinogenesis imperfecta), hearing loss and short stature.

There are 7 types of OI - they are due to changes (mutations) in the collagen genes (COL1A1 and COL1A2). These 2 genes are located on chromosomes 17 and 7. People with OI can be very mildly affected with only a few breaks in their bones or very severely affected.

Almost all types of OI have autosomal dominant inheritance. Anyone who has a mutation in one of the collagen genes has a 50% chance of passing that gene change on to each child. In your family, your dad passed it on to you.

Friedreich ataxia (FRDA) is a very different genetic disorder that leads to slow progressive ataxia (a loss of balance and problems coordinating movement of legs and walking) that usually starts in the mid teens. People with FRDA usually have absent reflexes in the legs, dysarthria – trouble swallowing or problems with speech, a loss of sensation in the lower legs and muscle weakness. People with FRDA can also have scoliosis (curvature of the spine), pes cavus (the breast bone sunken in), heart problems and glucose intolerance, or diabetes

FRDA is caused by a mutation (change) in a gene that is on chromosome 9. It is inherited in an autosomal recessive manner – that is both parents are carriers for the gene and are not affected, but have a 25% chance of both passing the mutated gene on at the same time and having an affected child.

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Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University